The present invention relates to foundry methods and equipment, and more particularly to a method and apparatus for combining high speed horizontal and high speed vertical continuous mixing of sand and binder ingredients for mold making purposes.
In the past, sand molds employed to cast metal objects have been produced by bonding the sand with clay, bentonite, sodium silicate or other such binders. Sand molds produced with these binders have generally been made by two different methods. One method involves pressing the sand/binder mixture into a metal flask which surrounds the mold during the molten metal pouring operation. A second method involves baking the sand mold to a hardened condition.
Recently, the foundry industry has begun to use a wide variety of quick setting resin binders. They have allowed sand molds of high quality to be rapidly produced without using metal flasks and without baking. Liquid binder ingredients (resin and catalyst) are mixed with sand and the mixture is poured into an open-top mold box containing a mold pattern. After being leveled and slightly compacted the mixture hardens in a relatively short time, e.g. 70 seconds. The hardening time depends upon the type of resin, the relative proportions of the ingredients, the temperature of the environment, etc. The completed mold may thereafter be removed or stripped from the mold box at which time it is ready for the molten metal pouring operation.
Conventional batch mullers have been used to mix sand, resin, and catalyst. Pre-measured quantities of the ingredients are poured into an open container and mixed by rotating blades. The average time needed for thorough mixing is generally on the order of several minutes. The mixture has a tendency to pre-cure in such batch mullers. If lumpy mixture is discharged into a mold box the resulting mold is unsuitable for casting. Furthermore, such batch mullers are incapable of continuously supplying sand/binder mixture. If a mold box requires more mixture than the batch size, additional batches must be prepared. The first batch poured into a mold box can harden before the second batch is poured over the same. The resulting sand mold is stratified and is unsuitable for casting.
Continuous mixers have recently become available to the foundry industry. Sand, binder and catalyst can be routed through these mixers and poured into mold boxes in a more or less continuous fashion. They generally incorporate one or more tubular mixing chambers each having a central rotating shaft which carries mixing blades. The shafts in various mixers are rotated at different speeds. As used herein, the term low speed refers to an rpm (revolutions per minute) of approximately 100 or less. The term high speed refers to an rpm of approximately 300 or more.
In a single stage continuous mixer, the sand, resin and catalyst are all mixed together in a single mixing chamber. This chamber is either horizontal or vertical, i.e. the blade carrying shaft extends either horizontally or vertically. In the case of a horizontal mixing chamber, the blade carrying shaft is rotated in some mixers at low speed and in other mixers at high speed. In the case of a vertical mixing chamber the blade carrying shaft is typically rotated at high speed.
In a two stage continuous mixer multiple mixing chambers are interconnected. The mixing chambers are either all horizontal or a combination of horizontal and vertical. In the former, the blade carrying shafts are all rotated at low speed in some mixers and are all rotated at high speed in other mixers. In the latter, the blade carrying shafts in the horizontal mixing chambers are rotated at low speed and the blade carrying shafts in the vertical mixing chambers are rotated at high speed. One sand mixer has utilized high speed pre-mixing in horizontal chambers which discharge into a slow speed vertical batch mixer. Heretofore, there has not been a method and apparatus for combining high speed horizontal and high speed vertical continuous mixing of sand and binder ingredients for mold making purposes.